The quest for high efficiency over a large peak to average power ratio (PAPR) and the ability to cover a wide bandwidth (BW) of operation (>160 MHz and typically >5% of carrier frequency) is desired for future high data rate wireless transmissions. Envelope Tracking (ET) has been demonstrated to provide high efficiency across >10 dB of PAPR for 20 MHz long term evolution (LTE) mobile applications. However, this approach is BW challenged and is strongly dependent on fundamental semiconductor technology trades. Bandwidths of up to 30 MHz have been demonstrated for mobile applications. Wireless Fidelity (Wi-Fi) BW requirements for 160 MHz 802.11 ac are challenging without costly semiconductor technology disruptions.
Doherty amplifiers can be configured to provide high efficiency over a 6 dB OPBO (output power back off or PAPR range). In particular, Doherty amplifiers may be configured to achieve larger PAPRs of 9 dB and 12 dB or more using N-way and/or asymmetric Doherty approaches. However, these are typically limited to operating BW<5% due to the narrow-band quarter wave impedance inverters used. Doherty amplifiers also rely on Digital Pre-Distortion (DPD) to correct for phase and amplitude distortion resulting from the Doherty operation. For base stations, DPD has shown operation up to 60 MHz with capability in the hundreds of MHz and exceeding 1 GHz for future point to point radio systems. However, Doherty amplifiers are not able to keep up with the BW capability of DPD.
Thus, what is needed is a new amplifier paradigm that is reconfigurable to provide the advantageous characteristics of Doherty amplifier operation while providing the BW capability of DPD. Moreover, an associated need is a load modulation type amplifier that is configured for improved OPBO efficiency by reducing impedance at lower power levels. It is important to note that this need is contrary to conventional load modulation amplifier approaches.